1. Field of the Invention
The invention relates to an endovascular graft prosthesis and an implantation method for such a prosthesis. More particularly, the invention relates to an endovascular split-tube bifurcated graft prosthesis and an implantation method for such a prosthesis.
2. Description of the Prior Art
Aortic aneurysms represent a significant medical problem for the general population. Aneurysms within the aorta presently affect between two and seven percent of the general population and the rate of incidence appears to be increasing. This form of atherosclerotic vascular disease (hardening of the arteries) is characterized by a degeneration in the arterial wall in which the wall weakens and balloons outward by thinning. An abdominal aortic aneurysm is a dilation of the main artery of the body. Until the affected artery is removed or bypassed, a patient with an abdominal aortic aneurysm ("AAA") must live with the threat of aortic aneurysm rupture and death. See Brody, J. E., "Aneurysm: A Potential Killer Lurking in the Aorta," The New York Times, Apr. 13, 1994, at C14.
One known clinical approach for patients with an abdominal aortic aneurysm is a surgical repair procedure. This is an extensive operation involving transperitoneal or retroperitoneal dissection of the aorta and replacement of the aneurysm with an artificial artery known as a prosthetic graft. This procedure requires a significant abdominal incision extending from the lower border of the breast bone down to the pubic bone to expose the abdominal aorta and the aneurysm so that the graft can be directly implanted. The operation requires a general anesthesia with a breathing tube, extensive intensive care unit monitoring in the immediate post-operative period, along with blood transfusions and stomach bladder tubes. All of this imposes stress on the cardiovascular system. Also associated with this procedure are well recognized morbidity (15%) and mortality (2-7%) rates. See Ernst, C. B. "Abdominal aortic Aneurysms," New England J. Med., Vol. 328: 1167-1172 (Apr. 22, 1993).
Today, there is the potential for a significantly less invasive clinical approach to aneurysm repair known as endovascular grafting. Parodi et al. provide one of the first clinical descriptions of this therapy. Parodi, J. C., et al., "Transfemoral Intraluminal Graft Implantation for Abdominal Aortic Aneurysms," 5 Annals of Vascular Surgery 491 (1991). Endovascular grafting involves the transluminal placement of a prosthetic arterial graft in the endoluminal position (within the lumen of the artery). By this method, the graft is attached to the internal surface of an arterial wall by means of attachment devices (expandable stents), one above the aneurysm and a second stent below the aneurysm.
Stents are devices that permit fixation of a graft to the internal surface of an arterial wall without sewing. Expansion of radially expandable stents is conventionally accomplished by dilating a balloon at the distal end of a balloon catheter. In U.S. Pat. No. 4,776,337, Palmaz describes a balloon-expandable stent which has received the greatest experimental and clinical application for endovascular treatments. Also known are self expanding stents, such as described in U.S. Pat. No. 4,655,771 to Wallsten.
Attachment of the stents above and below the aneurysm is a conceptually straightforward procedure when the aortic aneurysm is limited to the abdominal aorta and there are significant portions of normal tissue above and below the aneurysm (see FIG. 1). Unfortunately, 40-60% of aneurysms do not have suitable neck portions of normal tissue at the caudal portion (furthest from the head) of the aorta. Also, the severe tortuosity of the iliac arteries and the marked angulation of the aortoiliac junction compound the difficulty of fixing the stent in the caudal portion of the aorta. This situation is only exacerbated by the tendency of the abdominal aortic artery to elongate caudally during aneurysm formation. For want of sufficient normal aortic tissue to suitably attach a prosthetic graft at the caudal end of an aneurysm, or because of extension of the aneurysmal sac into the iliac arteries, bifurcated grafts have been developed that comprise a single body terminating with two limbs.
As a therapy to bypass an abdominal aortic aneurysm as well as any associated common iliac aneurysms, endoluminal deployment of a conventional bifurcated graft has presented significant issues to clinical operators in the field, primarily with respect to the positioning of one of the limbs of the graft in the contralateral iliac artery. The contralateral iliac artery is the artery that the conventional endoluminal bifurcated graft is not being advanced through. This procedure requires that both limbs of the graft be inserted into one branch of the femoral arterial system before being drawn or pulled over to the contralateral branch. This is to ensure that the graft is suitably positioned within the aorta and each of the right and left common iliac arteries. Even when tightly packaged, the bifurcated graft is a bulky device to advance through an often narrow single iliac artery.
The process of pulling one limb of the graft to the contralateral artery is time consuming and increases the risk of procedural complications, such as twisting and kinking of the graft-limb and injury to the vessel wall which can result in micro-embolization. As one limb of the graft is pulled across the frequently tortuous and twisted iliac artery anatomy, the graft may twist or kink. Any graft twist or kink may reduce or entirely cut-off blood flow to the arterial tree downstream thereof.
The procedure of drawing one limb of the prosthetic graft from one branch of the arterial system to the contralateral branch requires significant and skillful wire catheter manipulation within the aneurysmal cavity. See, for example, Chuter T. A. M., et al., "Transfemoral Endovascular Aortic Graft Placement," J. of Vascular Surgery 18: 185-190 (August, 1993). This procedure may result in micro-embolization of clots which are known to form within aneurysmal sacs. If these clots are disturbed or dislodged from the aortic aneurysm, they may break up into small fragments and flow downstream to other arteries. Excessive guide wire manipulation may also induce "churning" within the aneurysmal cavity which can cause proximal reflux or retrograde flow of thrombotic or embolic material into the arteries that supply circulation to the kidneys, intestines, and the liver.
Accordingly, there exists a need for a method for safely and effectively bypassing an aneurysm, such as an abdominal aortic aneurysm, located at or extending into a bifurcation in the vasculature, such as the common iliac arteries. There also exists the need for a guide wire which can be removed with minimal guide wire manipulation so as to prevent the above mentioned problem of "churning."
WO 95/16406 discloses an endovascular graft prosthesis for arrangement at or in the arterial system of a patient and comprising a substantially tubular main body for location in an upstream arteria above the bifurcation and substantially tubular legs joining said main body and extending via the bifurcation into each of two downstream branch arteries. This graft design avoids the problems inherent in forcing the entire graft through one of the narrow iliac arteries. One disadvantage of this prosthesis, however, is the complexity involved in making connections and achieving a good seal between the tubular legs and the main body.
U.S. Pat. No. 5,507,769 discloses an endoluminal bifurcated graft comprising two tubes each of which is advanced through the femoral and iliac arterial system on opposite sides of a patient's body. The distal ends of the tubes are aligned in a common region of normal aortic tissue above the aneurysm, after which "D" shaped vascular stents are deployed effectively locking the tubes in position and excluding blood from the aneurysmal cavity. One disadvantage of this prosthesis, however, is the complexity, and the resultant necessity for fluoroscopic assistance, in aligning the distal ends of each tube.
While these units may be suitable for the particular purpose employed, or for general use, they would not be as suitable for the purposes of the present invention as disclosed hereafter.